JP5313414B1 - Polymer piezoelectric material and manufacturing method thereof - Google Patents

Abstract

  In the present invention, a helical chiral polymer having an optical activity having a weight average molecular weight of 50,000 to 1,000,000, crystallinity obtained by DSC method is 20% to 80%, and microwave transmission molecule A polymeric piezoelectric material is provided in which the product of the normalized molecular orientation MORc and the crystallinity when the reference thickness measured by an orientation meter is 50 μm is 25 to 250.

Description

  The present invention relates to a polymer piezoelectric material and a method for producing the same.

Conventionally, PZT (PBZrO ₃ —PbTiO ₃ based solid solution), which is a ceramic material, has been widely used as the piezoelectric material. However, since PZT contains lead, currently, as a piezoelectric material, a polymer piezoelectric material having a low environmental load and high flexibility is being used.
Currently known polymer piezoelectric materials are mainly classified into the following two types. That is, Pauling type polymer represented by nylon 11, polyvinyl fluoride, polyvinyl chloride, polyurea, etc., polyvinylidene fluoride (β type) (PVDF), vinylidene fluoride-trifluoroethylene copolymer (P ( VDF-TrFE)) (75/25) and other ferroelectric polymers.

  However, polymeric piezoelectric materials are not as good as PZT in piezoelectricity, and are required to improve piezoelectricity. For this reason, attempts have been made to improve the piezoelectricity of the polymeric piezoelectric material from various viewpoints.

For example, the ferroelectric polymers PVDF and P (VDF-TrFE) have excellent piezoelectricity among the polymers, and the piezoelectric constant d ₃₁ is 20 pC / N or more. The film material formed from PVDF and P (VDF-TrFE), by orienting the polymer chain in the stretching direction by stretching operation, by giving different charges on the front and back of the film by corona discharge, An electric field is generated in the direction perpendicular to the film surface, and permanent dipoles containing fluorine in the side chains of the polymer chain are oriented parallel to the electric field direction to impart piezoelectricity. However, on the polarized film surface, foreign charges such as water and ions in the air tend to adhere in the direction that cancels the orientation, and the orientation of the permanent dipole aligned by the polarization treatment is relaxed, and the piezoelectricity over time. There has been a practical problem such as a noticeable decrease.

  PVDF is the most piezoelectric material among the above polymer piezoelectric materials, but the dielectric constant is relatively high among the polymer piezoelectric materials and is 13. Therefore, the piezoelectric d constant is divided by the dielectric constant. The value of the piezoelectric g constant (open voltage per unit stress) becomes small. Moreover, although PVDF has good conversion efficiency from electricity to sound, improvement in the conversion efficiency from sound to electricity has been expected.

  In recent years, attention has been paid to the use of polymers having optical activity, such as polypeptides and polylactic acid, in addition to the above-described polymeric piezoelectric materials. It is known that polylactic acid polymers exhibit piezoelectricity only by mechanical stretching operation. Among the polymers having optical activity, the piezoelectricity of a polymer crystal such as polylactic acid is attributed to a C = O bond permanent dipole that exists in the direction of the helical axis. In particular, polylactic acid has a small volume fraction of side chains with respect to the main chain and a large ratio of permanent dipoles per volume, and can be said to be an ideal polymer among the polymers having helical chirality. It is known that polylactic acid that exhibits piezoelectricity only by stretching treatment does not require poling treatment and the piezoelectricity does not decrease over several years.

  As described above, since polylactic acid has various piezoelectric characteristics, polymer piezoelectric materials using various polylactic acids have been reported. For example, a polymer piezoelectric material is disclosed that exhibits a piezoelectric constant of about 10 pC / N at room temperature by stretching a molded product of polylactic acid (see, for example, JP-A-5-152638). In addition, in order to make polylactic acid crystals highly oriented, it has also been reported that high piezoelectricity of about 18 pC / N is produced by a special orientation method called a forging method (see, for example, JP-A-2005-213376). .

However, since the piezoelectric material (film) shown in the above Japanese Patent Laid-Open Nos. 5-152638 and 2005-213376 is produced mainly by stretching in a uniaxial direction, it is easy to tear in a direction parallel to the stretching direction. There was a problem that the tear strength in a specific direction was low. Hereinafter, the tear strength in a specific direction is also referred to as “longitudinal tear strength”.
In addition, the piezoelectric materials disclosed in Japanese Patent Laid-Open Nos. 5-152638 and 2005-213376 are not sufficiently transparent.
In view of the above circumstances in the present invention, the piezoelectric constant d ₁₄ is large, excellent transparency, lowering of the vertical tear strength is an object to provide a polymeric piezoelectric material is suppressed and a manufacturing method thereof.

Specific means for achieving the above object are as follows.
[1] A helical chiral polymer having an optical activity with a weight average molecular weight of 50,000 to 1,000,000, crystallinity obtained by DSC method of 20% to 80%, and microwave transmission molecular orientation A polymer piezoelectric material, wherein the product of the normalized molecular orientation MORc and the crystallinity is 25 to 250 when the reference thickness measured by the meter is 50 μm.
[2] The polymeric piezoelectric material according to [1], wherein the crystallinity is 40.8% or less.
[3] The polymeric piezoelectric material according to [1] or [2], wherein the internal haze with respect to visible light is 40% or less.
[4] The polymeric piezoelectric material according to any one of [1] to [3], wherein the normalized molecular orientation MORc is 1.0 to 15.0.
[5] The piezoelectric constant _{d 14} measured by a displacement method at 25 ° C. is 1 Pm/V more, [1] polymeric piezoelectric material according to any one of - [4].
[6] The helical helical polymer according to any one of [1] to [5], wherein the helical chiral polymer is a polylactic acid polymer having a main chain containing a repeating unit represented by the following formula (1). Polymer piezoelectric material.

[7] The polymeric piezoelectric material according to any one of [1] to [6], wherein the helical chiral polymer has an optical purity of 95.00% ee or more.
[8] The polymeric piezoelectric material according to any one of [1] to [7], wherein the content of the helical chiral polymer is 80% by mass or more.
[9] The polymeric piezoelectric material according to any one of [1] to [8], wherein an internal haze with respect to visible light is 1.0% or less.
[10] A method for producing the polymeric piezoelectric material according to any one of [1] to [9], wherein the amorphous crystalline sheet containing the helical chiral polymer is heated to be pre-crystallized sheet And a second step of simultaneously stretching the pre-crystallized sheet in the biaxial direction.
[11] In the first step of obtaining the pre-crystallized sheet, the amorphous sheet is heated until the crystallinity becomes 1% to 70% at a temperature T represented by the following formula: [10 ] The manufacturing method of the polymeric piezoelectric material of description.
Tg−40 ° C. ≦ T ≦ Tg + 40 ° C.
(Tg represents the glass transition temperature of the helical chiral polymer.)
[12] In a first step of obtaining the pre-crystallized sheet, an amorphous sheet containing polylactic acid as the helical chiral polymer is heated at 20 ° C. to 170 ° C. for 5 seconds to 60 minutes. [10] Or the manufacturing method of the polymeric piezoelectric material as described in [11].
[13] The method for producing a polymeric piezoelectric material according to any one of [10] to [12], wherein annealing is performed after the second step.

According to the present invention, large piezoelectric constant d ₁₄ is excellent in transparency, longitudinal tear strength polymeric piezoelectric material decrease is suppressed in and a manufacturing method thereof can be provided.

The polymeric piezoelectric material of the present invention includes a helical chiral polymer having optical activity with a weight average molecular weight of 50,000 to 1,000,000 (hereinafter also referred to as “optically active polymer”), and is crystallized by a DSC method. The product of the normalized molecular orientation MORc and the crystallinity is 25 to 250 when the degree is 20% to 80% and the reference thickness measured by the microwave transmission type molecular orientation meter is 50 μm. is there.
The piezoelectric material by the above structure, large piezoelectric constant d ₁₄ is excellent in transparency, longitudinal tear strength can be a polymeric piezoelectric material decrease is suppressed in the (tear strength of the specific direction).
More specifically, in the polymer piezoelectric material having the above-described configuration, the crystallinity is in the range of 20% to 80%, and the product of the MORc and the crystallinity is 25 to 250. While maintaining the property (large piezoelectric constant d ₁₄ ) and high transparency, it is possible to suppress a phenomenon in which the longitudinal crack strength (the tear strength in a specific direction) decreases.

In the present specification, a decrease in tear strength in a specific direction is sometimes referred to as “longitudinal tear strength decreases”, and a state in which the tear strength in a specific direction is low is referred to as “longitudinal tear strength is low”. Sometimes.
In addition, in this specification, the phenomenon in which the tear strength in a specific direction is suppressed is sometimes referred to as “longitudinal tear strength is improved”, and the phenomenon in which the tear strength in a specific direction is decreased The suppressed state is sometimes referred to as “high longitudinal crack strength” or “excellent longitudinal crack strength”.

In the present embodiment, the “piezoelectric constant d ₁₄ ” is one of the tensors of the piezoelectric constant, and is based on the degree of polarization generated in the direction of the shear stress when a shear stress is applied in the direction of the stretching axis of the stretched material. Ask. Specifically, the generated charge density per unit shear stress is defined as d _14. Numerical piezoelectric constant d ₁₄ indicating that piezoelectricity is higher the larger. In the present specification, when simply referred to as “piezoelectric constant”, it means “piezoelectric constant d ₁₄ ”.

Here, the piezoelectric constant d ₁₄ is the value calculated by the following method.
That is, a rectangular film having a longitudinal direction at an angle of 45 ° with respect to the stretching direction is used as a test piece. An electrode layer is provided on the entire front and back of the main surface of the test piece, and when an applied voltage E (V) is applied to the electrode, the amount of strain in the longitudinal direction of the film is X. The value obtained by dividing the applied voltage E (V) by the film thickness t (m) is the electric field strength E (V / m), and the amount of strain in the longitudinal direction of the film when E (V) is applied is X. , _{d 14} is the value defined by 2 × strain amount X / field strength E (V / m).

The complex piezoelectric constant d ₁₄ is calculated as “d ₁₄ = d ₁₄ ′ −id ₁₄ ″”, and “d ₁₄ ′” and “id ₁₄ ″” are “Rheograph Solid S manufactured by Toyo Seiki Seisakusho Co., Ltd. -1 type ". “D ₁₄ ′” represents the real part of the complex piezoelectric constant, “id ₁₄ ″” represents the imaginary part of the complex piezoelectric constant, and d ₁₄ ′ (real part of the complex piezoelectric constant) represents the piezoelectric in the present embodiment. corresponding to the constant _{d 14.} In addition, it shows that it is excellent in piezoelectricity, so that the real part of complex piezoelectricity is high.
The piezoelectric constant d ₁₄ includes one measured by a displacement method (unit: pm / V) and one measured by a resonance method (unit: pC / N).

[Helical chiral polymer with optical activity]
The helical chiral polymer having optical activity refers to a polymer having molecular optical activity in which the molecular structure is a helical structure.
Hereinafter, the helical chiral polymer having optical activity having a weight average molecular weight of 50,000 to 1,000,000 is also referred to as “optically active polymer”.
Examples of the optically active polymer include polypeptides, cellulose, cellulose derivatives, polylactic acid resins, polypropylene oxide, poly (β-hydroxybutyric acid), and the like. Examples of the polypeptide include poly (glutarate γ-benzyl), poly (glutarate γ-methyl), and the like. Examples of the cellulose derivative include cellulose acetate and cyanoethyl cellulose.

  The optically active polymer preferably has an optical purity of 95.00% ee or higher, more preferably 99.00% ee or higher, from the viewpoint of improving the piezoelectricity of the polymeric piezoelectric material. More preferably, it is% ee or more. Desirably, it is 100.00% ee. By setting the optical purity of the optically active polymer within the above range, it is considered that the packing property of the polymer crystal that exhibits piezoelectricity is enhanced, and as a result, the piezoelectricity is enhanced.

In the present embodiment, the optical purity of the optically active polymer is a value calculated by the following formula.
Optical purity (% ee) = 100 × | L body weight−D body weight | / (L body weight + D body weight)
That is, “the amount difference (absolute value) between the amount of L-form [mass%] of optically active polymer and the amount of D-form [mass%] of optically active polymer” is expressed as The value obtained by multiplying (multiplying) the value obtained by dividing (dividing) the amount [mass%] by the total amount of the amount [mass%] of the optically active polymer D-form [mass%] and multiplying it by 100 And

  In addition, the value obtained by the method using a high performance liquid chromatography (HPLC) is used for the quantity [mass%] of the L body of an optically active polymer and the quantity [mass%] of the D body of an optically active polymer. Details of the specific measurement will be described later.

  Among the above optically active polymers, a compound having a main chain containing a repeating unit represented by the following formula (1) is preferable from the viewpoint of increasing optical purity and improving piezoelectricity.

  Examples of the compound having the repeating unit represented by the formula (1) as a main chain include polylactic acid resins. Among them, polylactic acid is preferable, and L-lactic acid homopolymer (PLLA) or D-lactic acid homopolymer (PDLA) is most preferable.

  The polylactic acid-based resin refers to “polylactic acid”, “copolymer of L-lactic acid or D-lactic acid and a copolymerizable polyfunctional compound”, or a mixture of both. The above-mentioned “polylactic acid” is a polymer in which lactic acid is polymerized by an ester bond and is connected for a long time, a lactide method via lactide, and a direct polymerization method in which lactic acid is heated in a solvent under reduced pressure and polymerized while removing water. It is known that it can be manufactured by, for example. Examples of the “polylactic acid” include L-lactic acid homopolymer, D-lactic acid homopolymer, block copolymer including at least one polymer of L-lactic acid and D-lactic acid, and L-lactic acid and D-lactic acid. Examples include graft copolymers containing at least one polymer.

  Examples of the “copolymerizable polyfunctional compound” include glycolic acid, dimethyl glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxypropanoic acid, 3-hydroxypropanoic acid, 2-hydroxyvaleric acid, 3 -Hydroxyvaleric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, 2-hydroxycaproic acid, 3-hydroxycaproic acid, 4-hydroxycaproic acid, 5-hydroxycaproic acid, 6-hydroxycaproic acid, 6-hydroxy Hydroxycarboxylic acids such as methyl caproic acid and mandelic acid, glycolides, cyclic esters such as β-methyl-δ-valerolactone, γ-valerolactone, and ε-caprolactone, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid , Pimelic acid, azelaic acid, sebacic acid, undecanedioic acid, Polycarboxylic acids such as candioic acid and terephthalic acid, and anhydrides thereof, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1 , 4-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, tetra Examples thereof include polyhydric alcohols such as methylene glycol and 1,4-hexanedimethanol, polysaccharides such as cellulose, and aminocarboxylic acids such as α-amino acids.

  Examples of the “copolymer of L-lactic acid or D-lactic acid and a copolymerizable polyfunctional compound” include a block copolymer or a graft copolymer having a polylactic acid sequence capable of forming a helical crystal.

  The concentration of the structure derived from the copolymer component in the optically active polymer is preferably 20 mol% or less. For example, when the optically active polymer is a polylactic acid polymer, the number of moles of the structure derived from lactic acid in the polylactic acid polymer and the structure derived from a compound copolymerizable with lactic acid (copolymer component) It is preferable that the copolymer component is 20 mol% or less based on the total.

The optically active polymer (for example, polylactic acid-based resin) is obtained by, for example, a method obtained by directly dehydrating and condensing lactic acid described in JP-A-59-096123 and JP-A-7-033861. It can be produced by a ring-opening polymerization method using lactide, which is a cyclic dimer of lactic acid, described in Patents 2,668,182 and 4,057,357.
Furthermore, the optically active polymer (for example, polylactic acid-based resin) obtained by each of the above production methods has an optical purity of 95.00% ee or more, for example, when polylactic acid is produced by the lactide method, It is preferable to polymerize lactide whose optical purity is improved to 95.00% ee or higher by crystallization operation.

[Weight average molecular weight of optically active polymer]
The optically active polymer according to this embodiment has a weight average molecular weight (Mw) of 50,000 to 1,000,000. If the lower limit of the weight average molecular weight of the optically active polymer is less than 50,000, the mechanical strength when the optically active polymer is molded is insufficient. The lower limit of the weight average molecular weight of the optically active polymer is preferably 100,000 or more, and more preferably 150,000 or more. On the other hand, when the upper limit of the weight average molecular weight of the optically active polymer exceeds 1,000,000, it becomes difficult to mold the optically active polymer (for example, to form a film shape by extrusion molding or the like).
The upper limit of the weight average molecular weight is preferably 800,000 or less, and more preferably 300,000 or less.
The molecular weight distribution (Mw / Mn) of the optically active polymer is preferably 1.1 to 5, and more preferably 1.2 to 4, from the viewpoint of the strength of the polymer piezoelectric material. Furthermore, it is preferable that it is 1.4-3. The weight average molecular weight Mw and molecular weight distribution (Mw / Mn) of the polylactic acid polymer are measured by gel permeation chromatography (GPC) by the following GPC measurement method.

-GPC measuring device-
Waters GPC-100
-Column-
Made by Showa Denko KK, Shodex LF-804
-Sample preparation-
A polylactic acid polymer is dissolved in a solvent (for example, chloroform) at 40 ° C. to prepare a sample solution having a concentration of 1 mg / ml.
-Measurement conditions-
0.1 ml of the sample solution is introduced into the column at a solvent [chloroform], a temperature of 40 ° C., and a flow rate of 1 ml / min.

  The sample concentration in the sample solution separated by the column is measured with a differential refractometer. A universal calibration curve is created with a polystyrene standard sample, and the weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the polylactic acid polymer are calculated.

  Commercially available polylactic acid may be used as the polylactic acid polymer. Examples of commercially available polylactic acid include PURASORB (PD, PL) manufactured by PURAC, LACEA (H-100, H-400) manufactured by Mitsui Chemicals, Ingeo 4032D, 4043D manufactured by NatureWorks, and the like.

  When a polylactic acid resin is used as the optically active polymer, the optically active polymer should be produced by the lactide method or the direct polymerization method in order to increase the weight average molecular weight (Mw) of the polylactic acid resin to 50,000 or more. Is preferred.

The polymeric piezoelectric material according to this embodiment may contain only one kind of the optically active polymer described above, or may contain two or more kinds.
In the polymeric piezoelectric material according to the present embodiment, the content of the optically active polymer (the total content when there are two or more types; the same shall apply hereinafter) is not particularly limited, but is within the total mass of the polymeric piezoelectric material. It is preferable that it is 80 mass% or more.
When the content is 80% by mass or more, the piezoelectric constant tends to be larger.

[Other ingredients]
The polymer piezoelectric material of the present embodiment is a known component represented by other components (for example, polyvinylidene fluoride, polyethylene resin, and polystyrene resin) other than the optically active polymer described above, as long as the effects of the present embodiment are not impaired. Or a known crystal nucleating agent such as phthalocyanine, or the like, or a silica, hydroxyapatite, montmorillonite, or the like.
Moreover, it is preferable that the polymeric piezoelectric material of this embodiment contains stabilizers, such as a carbodiimide compound represented by the carbodilite (trademark) from a viewpoint of suppressing the structural change by hydrolysis etc. more.
In addition, the polymeric piezoelectric material of the present embodiment has the above-described optically active polymer (that is, an optical activity having a weight average molecular weight (Mw) of 50,000 to 1,000,000) as long as the effects of the present embodiment are not impaired. A helical chiral polymer other than the helical chiral polymer may be included.

-Inorganic filler-
The polymeric piezoelectric material of this embodiment may contain at least one inorganic filler.
For example, an inorganic filler such as hydroxyapatite may be nano-dispersed in the polymer piezoelectric material in order to make the polymer piezoelectric material a transparent film in which the generation of voids such as bubbles is suppressed. In order to make nano-dispersion, a large energy is required for crushing the aggregate, and when the inorganic filler is not nano-dispersed, the transparency of the film may be lowered. Therefore, when the polymeric piezoelectric material according to the present embodiment contains an inorganic filler, the content of the inorganic filler with respect to the total mass of the polymeric piezoelectric material is preferably less than 1% by mass. When the polymer piezoelectric material contains a component other than the optically active polymer, the content of the component other than the optically active polymer is preferably 20% by mass or less based on the total mass of the polymer piezoelectric material. More preferably, it is 10 mass% or less.

-Crystal accelerator (crystal nucleating agent)-
The polymeric piezoelectric material of the present embodiment may contain at least one crystallization accelerator (crystal nucleating agent).
The crystal accelerator (crystal nucleator) is not particularly limited as long as the effect of promoting crystallization is recognized, but is a substance having a crystal structure having a face spacing close to the face spacing of the crystal lattice of the optically active polymer. It is desirable to select. This is because a substance with a close spacing is more effective as a nucleating agent. For example, when polylactic acid resin is used as the optically active polymer, organic materials such as zinc phenylsulfonate, melamine polyphosphate, melamine cyanurate, zinc phenylphosphonate, calcium phenylphosphonate, magnesium phenylphosphonate, inorganic Examples thereof include talc and clay. Among them, zinc phenylphosphonate is most preferable because the face spacing is most similar to the face spacing of polylactic acid and provides a good crystal formation promoting effect. In addition, the commercially available crystal accelerator can be used. Specific examples include zinc phenylphosphonate; Eco Promote (manufactured by Nissan Chemical Industries, Ltd.) and the like.

The content of the crystal nucleating agent is usually 0.01 to 1.0 part by weight, preferably 0.01 to 0.5 part by weight, based on 100 parts by weight of the optically active polymer. The amount is particularly preferably 0.02 to 0.2 parts by weight from the viewpoint of maintenance.
When the content of the crystal nucleating agent is 0.01 parts by weight or more, the effect of promoting crystallization can be obtained more effectively. When the content of the crystal nucleating agent is less than 1.0 part by weight, the crystallization rate can be more easily controlled.

  In addition, it is preferable that a polymeric piezoelectric material does not contain components other than the helical chiral polymer | macromolecule which has optical activity from a transparency viewpoint.

〔Construction〕
In the polymer piezoelectric material of the present embodiment, the optically active polymer is oriented.
As an index representing this orientation, there is a “molecular orientation degree MOR”. The molecular orientation degree MOR (Molecular Orientation Ratio) is a value indicating the degree of molecular orientation, and is measured by the following microwave measurement method. That is, the sample surface (film surface) is placed in a microwave resonant waveguide of a well-known microwave molecular orientation measuring apparatus (also referred to as a microwave transmission type molecular orientation meter) in the microwave traveling direction. ) To be vertical. Then, in a state where the sample is continuously irradiated with the microwave whose vibration direction is biased in one direction, the sample is rotated by 0 to 360 ° in a plane perpendicular to the traveling direction of the microwave, and the microwave transmitted through the sample is transmitted. The degree of molecular orientation MOR is determined by measuring the strength.

The normalized molecular orientation MORc in the present embodiment is a MOR value when the reference thickness tc is 50 μm, and can be obtained by the following equation.
MORc = (tc / t) × (MOR-1) +1
(Tc: reference thickness to be corrected, t: sample thickness)
The normalized molecular orientation MORc can be measured with a known molecular orientation meter such as a microwave molecular orientation meter MOA-2012A or MOA-6000 manufactured by Oji Scientific Instruments Co., Ltd., at a resonance frequency in the vicinity of 4 GHz or 12 GHz.

  In addition, the normalized molecular orientation MORc can be controlled by the crystallization conditions (for example, heating temperature and heating time) and the stretching conditions (for example, stretching temperature and stretching speed) in producing the polymeric piezoelectric material.

The normalized molecular orientation MORc can be converted into a birefringence Δn obtained by dividing the retardation amount (retardation) by the thickness of the film.
Specifically, retardation can be measured using RETS100 manufactured by Otsuka Electronics Co., Ltd. MORc and Δn are approximately in a linear proportional relationship, and when Δn is 0, MORc is 1.

<Physical properties of polymer piezoelectric material>
Polymeric piezoelectric material according to this embodiment, the piezoelectric constant is increased (piezoelectric constant d ₁₄ measured by a displacement method at 25 ° C. is preferably 1 Pm/V or more), excellent transparency, longitudinal tear strength.

[Piezoelectric constant (displacement method)]
In the present embodiment, the piezoelectric constant of the polymeric piezoelectric material is a value measured as follows.
First, the polymeric piezoelectric material is cut at 40 mm in the stretching direction (MD direction) and 40 mm in the direction orthogonal to the stretching direction (TD direction) to produce a rectangular test piece. Next, the obtained test piece is set on a test stand of a sputtering thin film forming apparatus JSP-8000 manufactured by ULVAC, and the coater chamber is evacuated (for example, 10 ⁻³ Pa or less) by a rotary pump. Thereafter, sputtering is performed on one surface of the test piece for 500 seconds on an Ag (silver) target under the conditions of an applied voltage of 280 V and a sputtering current of 0.4 A). Next, the other surface of the test piece is sputtered for 500 seconds under the same conditions to coat Ag on both sides of the test piece to form an Ag conductive layer.

  A 40 mm × 40 mm test piece (polymer piezoelectric material) having an Ag conductive layer formed on both sides is formed in a direction of 45 mm and a direction of 45 ° with respect to the stretching direction (MD direction) of the polymer piezoelectric material. Cut to 5 mm in an orthogonal direction, and cut out a rectangular film of 32 mm × 5 mm. This is a piezoelectric constant measurement sample.

The difference distance between the maximum value and the minimum value of the displacement of the film when a sinusoidal AC voltage of 10 Hz and 300 Vpp is applied to the obtained sample is measured with a laser spectral interference displacement meter SI-1000 manufactured by Keyence Corporation. .
The value obtained by dividing the measured displacement (mp-p) by the reference length of the film 30 mm is used as the amount of strain, and the amount of strain is expressed by the electric field intensity ((applied voltage (V)) / (film thickness)) applied to the film. the value obtained by multiplying 2 to the value obtained by dividing a piezoelectric constant d _14.

The higher the piezoelectric constant, the greater the displacement of the material with respect to the voltage applied to the polymer piezoelectric material, and conversely the greater the voltage generated against the force applied to the polymer piezoelectric material, which is useful as a polymer piezoelectric material. It is.
Specifically, is preferably at least 1 Pm/V piezoelectric constant _{d 14} is measured by a displacement method at 25 ° C., more preferably at least 3pm / V, more preferably not less than 4pm / V. The upper limit of the piezoelectric constant is not particularly limited, but from the viewpoint of balance such as transparency described later, the piezoelectric material using the helical chiral polymer is preferably 50 pm / V or less, and more preferably 30 pm / V or less.
From the viewpoint of the balance with similarly transparency is preferably a piezoelectric constant d ₁₄ measured by a resonance method is not more than 15pC / N.

  In the present specification, the “MD direction” is a direction in which the film flows (Machine Direction), and the “TD direction” is a direction perpendicular to the MD direction and parallel to the main surface of the film (Transverse Direction). ).

[Crystallinity]
The crystallinity of the polymer piezoelectric material is determined by the DSC method, and the crystallinity of the polymer piezoelectric material of the present embodiment is 20% to 80%, preferably 30% to 70%. When the crystallinity is within the above range, the piezoelectricity, transparency, and longitudinal tear strength of the polymeric piezoelectric material are well balanced, and when the polymeric piezoelectric material is stretched, whitening and breakage are unlikely to occur and it is easy to manufacture.
Specifically, when the crystallinity is less than 20%, the piezoelectricity tends to decrease.
On the other hand, if the crystallinity exceeds 80%, the longitudinal crack strength and transparency tend to decrease.
The crystallinity is more preferably 40.8% or less, and particularly preferably 40.0% or less, from the viewpoint of further improving the longitudinal crack strength and transparency.

  In the present embodiment, for example, the crystallinity of the polymer piezoelectric material can be adjusted to a range of 20% to 80% by adjusting the crystallization and stretching conditions when the polymer piezoelectric material is manufactured. .

[Transparency (internal haze)]
The transparency of the polymeric piezoelectric material can be evaluated, for example, by visual observation or haze measurement.
The polymeric piezoelectric material preferably has an internal haze with respect to visible light of 40% or less. Here, the internal haze is a haze measuring instrument [Tokyo Denshoku Co., Ltd., TC-HIII DPK] in accordance with JIS-K7105 for a polymer piezoelectric material having a thickness of 0.03 mm to 0.05 mm. It is a value when it is used and measured at 25 ° C., and details of the measuring method will be described in detail in Examples.
The internal haze of the polymeric piezoelectric material is more preferably 20% or less, and further preferably 5% or less. Further, the internal haze of the polymeric piezoelectric material is preferably 2.0% or less, and particularly preferably 1.0% or less, from the viewpoint of further improving the longitudinal crack strength.
The lower the internal haze of the polymeric piezoelectric material, the better. However, from the viewpoint of balance with the piezoelectric constant, etc., it is preferably 0.0% to 40%, and 0.01% to 20%. Is more preferable, 0.01% to 5% is more preferable, 0.01% to 2.0% is further preferable, and 0.01% to 1.0% is particularly preferable.
As used herein, “internal haze” refers to the internal haze of the polymeric piezoelectric material of the present invention. The internal haze is haze excluding haze due to the shape of the outer surface of the polymeric piezoelectric material, as will be described later in Examples.

[Standardized molecular orientation MORc]
The polymer piezoelectric material of the present embodiment preferably has a normalized molecular orientation MORc of 1.0 to 15.0, and more preferably 4.0 to 10.0.
If the normalized molecular orientation MORc is 1.0 or more, there are many optically active polymer molecular chains (for example, polylactic acid molecular chains) arranged in the stretching direction, and as a result, the rate of formation of oriented crystals increases. High piezoelectricity can be expressed.
If the normalized molecular orientation MORc is 15.0 or less, the longitudinal crack strength is further improved.

[Product of normalized molecular orientation MORc and crystallinity]
In this embodiment, the product of the crystallinity of the polymeric piezoelectric material and the normalized molecular orientation MORc is 25-250. By adjusting to this range, high piezoelectricity and high transparency are maintained, and a decrease in longitudinal tear strength (that is, tear strength in a specific direction) is suppressed.
If the product of the crystallinity of the polymeric piezoelectric material and the normalized molecular orientation MORc is less than 25, the piezoelectricity tends to decrease.
When the product of the crystallinity of the polymeric piezoelectric material and the normalized molecular orientation MORc exceeds 250, the longitudinal crack strength and transparency tend to decrease.
The product of the crystallinity and MORc is more preferably 50 to 200, and still more preferably 100 to 190.

  In the present embodiment, for example, by adjusting the crystallization and stretching conditions in manufacturing the polymer piezoelectric material, the product of the crystallinity of the polymer piezoelectric material and the normalized molecular orientation MORc is 25 to 250. Can be adjusted to the range.

(Longitudinal crack strength)
The longitudinal tear strength of the polymeric piezoelectric material of the present embodiment is measured according to the test method “Right-angle tear method” described in “Plastic film and sheet tear strength” of JIS K 7128-3. It is evaluated based on strength.
Here, the crosshead speed of the tensile tester is 200 mm per minute, and the tear strength is calculated from the following equation.
T = F / d
In the above formula, T represents the tear strength (N / mm), F represents the maximum tear load, and d represents the thickness (mm) of the test piece.

(Dimensional stability)
It is preferable that the piezoelectric polymer material has a low dimensional change rate at a temperature under heating, particularly in an environment in which it is incorporated and used in a device or device such as a speaker or a touch panel described later. This is because if the dimensions of the piezoelectric material change in the environment of use of the device or the like, the position of the wiring or the like connected to the piezoelectric material may be moved to cause malfunction of the device or the like. As will be described later, the dimensional stability of the polymeric piezoelectric material is evaluated by the dimensional change rate before and after being treated for 10 minutes at 150 ° C., which is a temperature slightly higher than the usage environment of the device. The dimensional change rate is preferably 10% or less, and more preferably 5% or less.

<Manufacture of polymer piezoelectric material>
As a method for producing the polymeric piezoelectric material of the present invention, the crystallinity can be adjusted to 20% to 80%, and the product of the normalized molecular orientation MORc and the crystallinity can be adjusted to 25 to 250. There is no particular limitation as long as it can be performed.
As this method, for example, crystallization and stretching (any of which may be the first) are performed on an amorphous sheet containing the optically active polymer described above, and the crystallization and stretching By adjusting each of the above conditions, the crystallinity is adjusted to 20% to 80%, and the product of the normalized molecular orientation MORc and the crystallinity is adjusted to 25 to 250. Can do.
Here, “crystallization” is a concept including preliminary crystallization described later and annealing treatment described later.

  The non-crystalline sheet refers to a sheet obtained by heating an optically active polymer alone or a mixture containing an optically active polymer to a temperature equal to or higher than the melting point Tm of the optically active polymer and then rapidly cooling it. . An example of the rapid cooling temperature is 50 ° C.

In the method for producing a polymeric piezoelectric material of the present invention, the optically active polymer (such as polylactic acid polymer) is used alone as a raw material for the polymeric piezoelectric material (or amorphous sheet). Alternatively, a mixture of two or more of the optically active polymers described above (such as polylactic acid polymers), or a mixture of at least one of the optically active polymers described above and at least one of the other components. May be used.
The above mixture is preferably a mixture obtained by melt kneading.
Specifically, for example, when mixing two or more types of optically active polymers, or when mixing other components (for example, the above-described inorganic filler and crystal nucleating agent) with one or more types of optically active polymers, The optically active polymer to be mixed (along with other components as necessary) is 5 using a melt kneader (manufactured by Toyo Seiki Co., Ltd., Labo Plast Mixer) under the conditions of a mixer rotational speed of 30 rpm to 70 rpm and 180 ° C. to 250 ° C. By melt-kneading for 20 minutes for 20 minutes, a blend of a plurality of types of optically active polymers or a blend of optically active polymers and other components such as inorganic fillers can be obtained.

  Hereinafter, although the embodiment of the manufacturing method of the polymeric piezoelectric material of the present invention will be described, the method of manufacturing the polymeric piezoelectric material of the present invention is not limited to the following embodiment.

-First embodiment-
The first embodiment of the method for producing a polymeric piezoelectric material of the present invention includes, for example, an optically active polymer (that is, a helical chiral polymer having optical activity having a weight average molecular weight of 50,000 to 1,000,000). A first step of heating a crystallized sheet to obtain a pre-crystallized sheet, and stretching the pre-crystallized sheet in a biaxial direction (for example, stretching the uniaxial direction while simultaneously or sequentially stretching Extending in a direction different from the direction).

In general, increasing the force applied to the film during stretching promotes the orientation of the optically active polymer and increases the piezoelectric constant, while crystallization progresses and the crystal size increases, so that the internal haze increases. There is a tendency. Also, the dimensional deformation rate tends to increase due to an increase in internal stress. If force is simply applied to the film, crystals that are not oriented like spherulites are formed. A crystal having a low orientation such as a spherulite increases the internal haze, but hardly contributes to an increase in piezoelectric constant.
Therefore, in order to form a film having a high piezoelectric constant and a low internal haze, it is preferable to efficiently form oriented crystals that contribute to the piezoelectric constant with a minute size that does not increase the internal haze.

From the above points, for example, after preparing the pre-crystallized sheet in which the inside of the sheet is pre-crystallized to form fine crystals (microcrystals) before stretching, the pre-crystallized sheet is stretched, thereby The stretching force can be efficiently applied to the polymer portion having low crystallinity between the microcrystals in the crystallized sheet. Thereby, the optically active polymer can be efficiently oriented in the main stretching direction.
Specifically, by stretching the pre-crystallized sheet, finely oriented crystals are formed in the polymer portion having low crystallinity between the microcrystals and at the same time generated by pre-crystallization. The spherulites are broken, and the lamellar crystals constituting the spherulites are oriented in the stretching direction in a daisy chain connected to the tie molecular chain. As a result, a desired value of MORc can be obtained.
For this reason, by extending | stretching the said precrystallized sheet, a sheet | seat with a low internal haze can be obtained, without reducing a piezoelectric constant largely. Furthermore, a polymer piezoelectric material having excellent dimensional stability can be obtained by adjusting the manufacturing conditions.

  However, in the method of stretching the pre-crystallized sheet, the polymer chains in the low-crystallinity portion inside the pre-crystallized sheet are unwound by stretching, and the molecular chains are aligned in the stretch direction. Although the tear strength with respect to the force from is improved, the tear strength with respect to the force from the direction substantially parallel to the stretching direction may be decreased.

In view of the above points, in the first embodiment, a first step of obtaining a pre-crystallized sheet by heating an amorphous sheet containing an optically active polymer, and the pre-crystallized sheet in a biaxial direction. And a second step of stretching.
In the first embodiment, in the second step (stretching step), when the pre-crystallized sheet is stretched (also referred to as main stretching) in order to enhance piezoelectricity, the stretching direction of the main stretching is simultaneously or sequentially performed. Biaxial stretching is performed in which the pre-crystallized sheet is stretched (also referred to as secondary stretching) in the direction intersecting with. Thereby, since the molecular chain in the sheet can be oriented not only in the direction of the main stretching axis but also in the direction intersecting with the main stretching axis, the normalized molecular orientation MORc and the crystallinity The product can be suitably adjusted to a specific range (specifically 25 to 250).
As a result, it is possible to increase the longitudinal crack strength while enhancing the piezoelectricity and maintaining the transparency.

In order to control the normalized molecular orientation MORc, it is important to adjust the heating time and heating temperature of the amorphous sheet in the first step, and the stretching speed and stretching temperature of the pre-crystallized sheet in the second step. is there.
As described above, the optically active polymer is a polymer having molecular optical activity in which the molecular structure is a helical structure.
The amorphous sheet containing the optically active polymer may be commercially available, or may be produced by a known film forming means such as extrusion. The amorphous sheet may be a single layer or a multilayer.

[First step (pre-crystallization step)]
The first step in the first embodiment is a step of obtaining a pre-crystallized sheet by heating an amorphous sheet containing an optically active polymer.

  Specifically, as the treatment through the first step and the second step in the first embodiment, 1) a non-crystalline sheet is heat-treated to form a pre-crystallized sheet (the first step). The obtained pre-crystallized sheet may be set in a drawing apparatus and drawn (second step), or (off-line processing), or 2) the amorphous sheet is drawn into the drawing apparatus. Set and heated in a stretching device to form a pre-crystallized sheet (above, the first step), and the obtained pre-crystallized sheet is subsequently stretched in the stretching device (above, the second step). There may be (inline processing).

In the first step, the heating temperature T for pre-crystallizing the amorphous state sheet containing the optically active polymer is not particularly limited. However, in terms of enhancing the piezoelectricity and transparency of the polymer piezoelectric material to be produced. The glass transition temperature Tg of the optically active polymer and the following formula are preferably satisfied, and the crystallinity is preferably set to 1 to 70%.
Tg−40 ° C. ≦ T ≦ Tg + 40 ° C.
(Tg represents the glass transition temperature of the optically active polymer.)

  Here, the glass transition temperature Tg [° C.] of the optically active polymer and the melting point Tm [° C.] of the optically active polymer mentioned above are calculated with respect to the optically active polymer using the above-mentioned differential scanning calorimeter (DSC). Thus, from the melting endothermic curve when the temperature is increased at a temperature rising rate of 10 ° C./min, the glass transition temperature (Tg) obtained as the inflection point of the curve and the temperature confirmed as the peak value of the endothermic reaction ( Tm).

  In the first step, the heat treatment time for pre-crystallization satisfies the desired crystallinity and the normalized molecular orientation MORc of the polymer piezoelectric material after stretching (after the second step) and the stretched What is necessary is just to adjust so that the product with the crystallinity degree of a polymeric piezoelectric material may be 25-250, Preferably it is 50-200, More preferably, it is 100-190. As the heat treatment time becomes longer, the degree of crystallinity after stretching increases, and the normalized molecular orientation MORc after stretching also increases. When the heat treatment time is shortened, the degree of crystallinity after stretching also decreases, and the normalized molecular orientation MORc after stretching also decreases.

  When the degree of crystallization of the pre-crystallized sheet before stretching increases, the sheet becomes harder and a greater stretching stress is applied to the sheet, so that the portion with relatively low crystallinity in the sheet also becomes more oriented, and after stretching It is considered that the normalized molecular orientation MORc also increases. On the contrary, when the crystallinity of the pre-crystallized sheet before stretching becomes low, the sheet becomes soft and the stretching stress becomes more difficult to be applied to the sheet, so that the portion with relatively low crystallinity in the sheet becomes weakly oriented. The normalized molecular orientation MORc after stretching is also considered to be low.

  The heat treatment time varies depending on the kind or amount of the heat treatment temperature, the thickness of the sheet, the molecular weight of the resin constituting the sheet, and the additive. In addition, the substantial heat treatment time for crystallizing the sheet is the preheating that may be performed before the stretching step (second step) described later, and when the amorphous sheet is preheated at a temperature for crystallization, This corresponds to the sum of the preheating time and the heat treatment time in the precrystallization step before preheating.

  The heat treatment time for the amorphous sheet is preferably from 5 seconds to 60 minutes, and more preferably from 1 minute to 30 minutes from the viewpoint of stabilizing the production conditions. For example, in the case of pre-crystallizing an amorphous sheet containing a polylactic acid resin as an optically active polymer, it may be heated at 20 ° C. to 170 ° C. for 5 seconds to 60 minutes (preferably 1 minute to 30 minutes). preferable.

In the first embodiment, in order to efficiently impart piezoelectricity, transparency, and longitudinal crack strength to the stretched sheet, it is preferable to adjust the crystallinity of the precrystallized sheet before stretching.
That is, the reason why the piezoelectricity and the like are improved by stretching is that the spherulite is presumed to be in a spherulitic state, stress due to stretching is concentrated in a portion having a relatively high crystallinity in the pre-crystallized sheet, and the spherulites are being destroyed. Orientation improves the piezoelectricity (piezoelectric constant d ₁₄ ), while stretching stress is applied to a portion having a relatively low crystallinity via the spherulite, and the orientation of the relatively low portion is promoted, and piezoelectricity (piezoelectricity) This is because the constant d ₁₄ ) is considered to be improved.

  The degree of crystallinity of the stretched sheet is set to 20% to 80%, preferably 30% to 70%. Therefore, the crystallinity immediately before stretching of the pre-crystallized sheet is set to be 1% to 70%, preferably 2% to 60%. The crystallinity of the pre-crystallized sheet may be the same as the measurement of the crystallinity of the polymer piezoelectric material of the present embodiment after stretching.

  The thickness of the pre-crystallized sheet is mainly determined by the thickness of the polymeric piezoelectric material to be obtained by stretching in the second step and the stretching ratio, but is preferably 50 μm to 1000 μm, more preferably about 200 μm to 800 μm. It is.

[Second step (stretching step)]
The stretching method in the second step (stretching step) is not particularly limited. Stretching for forming oriented crystals (also referred to as main stretching) and stretching performed in a direction intersecting the direction of stretching. A combined method can be used. By stretching the polymer piezoelectric material, a polymer piezoelectric material having a large principal surface area can be obtained.

  Here, the “main surface” refers to the surface having the largest area among the surfaces of the polymeric piezoelectric material. The polymeric piezoelectric material of the present invention may have two or more principal surfaces. For example, when the polymer piezoelectric material is a plate-like body having two surfaces A each having a surface A of 10 mm × 0.3 mm square, a surface B having 3 mm × 0.3 mm square, and a surface C having 10 mm × 3 mm square. The main surface of the polymeric piezoelectric material is a surface C, which has two main surfaces.

As for the area of the main surface in the present embodiment, the area of the main surface of the polymeric piezoelectric material is preferably 5 mm ² or more, and more preferably 10 mm ² or more.

By stretching the polymer piezoelectric material mainly in one direction, the molecular chain of polylactic acid polymer contained in the polymer piezoelectric material can be oriented in one direction and aligned with high density, which is higher It is estimated that piezoelectricity can be obtained.
On the other hand, when stretched in only one direction as described above, the molecular chain of the polymer in the sheet is mainly oriented in the stretching direction, so that there is a risk that the longitudinal crack strength due to the force from the direction substantially perpendicular to the stretching direction is lowered. is there.
Therefore, in the stretching process, when stretching for enhancing piezoelectricity (also referred to as main stretching), simultaneously or sequentially, the pre-crystallized sheet is stretched in a direction crossing the main stretching direction (secondary stretching). By performing biaxial stretching (also referred to as stretching), a polymer piezoelectric material having an excellent balance of piezoelectricity, transparency, and longitudinal crack strength can be obtained.
Here, “sequential stretching” refers to a stretching method in which stretching is performed in a uniaxial direction and then stretching in a direction intersecting with the stretching direction.

The biaxial stretching method in the second step is not particularly limited, and a general method can be used. Specifically, roll stretching (stretching in the MD direction) and tenter stretching (stretching in the TD direction). It is preferable to use a combination of these. At this time, from the viewpoint of production efficiency, it is preferable to set the direction in which the stretching ratio is large (for example, the main stretching direction) to the TD direction and the direction in which the stretching ratio is low (for example, the secondary stretching direction) to the MD direction.
Biaxial stretching may be performed simultaneously or sequentially, but is preferably performed simultaneously (that is, simultaneous biaxial stretching).
The reason why simultaneous biaxial stretching is preferable is that, in the case of sequential stretching, in the second and subsequent stretching, a force is applied in a direction crossing the direction of the first stretching, so that the film is longitudinally split during stretching. Because there is a fear.
Similarly, when performing sequential stretching, it is preferable to reduce the stretching ratio performed first from the viewpoint of suppressing longitudinal tearing of the film during the second and subsequent stretching.
As described above, the “MD direction” is a direction in which the film flows, and the “TD direction” is a direction perpendicular to the MD direction and parallel to the main surface of the film.

The draw ratio can be adjusted so that the product of the crystallinity, MORc, and crystallinity of the polymeric piezoelectric material after stretching (or after annealing if an annealing process described later) is within the above-mentioned range. Although not particularly limited, the draw ratio of main stretching is preferably 2 to 8 times, more preferably 2.5 to 5 times, and particularly preferably 2.7 to 4.5 times. Further, the draw ratio of the secondary stretching is preferably 1 to 4 times, more preferably 1.2 to 2.5 times, and more preferably 1.2 to 2.3 times.
Also, the stretching speed is not particularly limited, but usually, the main stretching speed and the secondary stretching speed are adjusted according to the magnification. Specifically, when the main stretching ratio is set to twice the secondary stretching ratio, the main stretching speed is often set to twice the secondary stretching. The stretching speed may be set to a speed usually used, and is not particularly limited, but is often adjusted to a speed at which the film does not break during stretching.

  The stretching temperature of the polymeric piezoelectric material is 10 ° C. to 20 ° C. from the glass transition temperature of the polymeric piezoelectric material when the polymeric piezoelectric material is stretched only by a tensile force, such as a uniaxial stretching method or a biaxial stretching method. It is preferable that the temperature range be as high as about ° C.

When the pre-crystallized sheet is stretched, preheating may be performed immediately before stretching in order to facilitate stretching of the sheet.
This preheating is generally performed in order to soften the sheet before stretching and facilitate stretching, so that the sheet before stretching is crystallized and does not harden the sheet. It is normal.
However, as described above, in the first embodiment, since pre-crystallization is performed before stretching, the pre-heating may be performed together with pre-crystallization. Specifically, preheating and precrystallization can be performed by performing preheating at a temperature higher or longer than the normal temperature in accordance with the heating temperature and heat treatment time in the precrystallization step described above.

[Annealing process]
From the viewpoint of improving the piezoelectric constant, it is preferable that the polymer piezoelectric material after the stretching treatment is subjected to a certain heat treatment (hereinafter also referred to as “annealing treatment”). The temperature of the annealing treatment is preferably about 80 ° C to 160 ° C, and more preferably 100 ° C to 155 ° C.
The temperature application method for the annealing treatment is not particularly limited, and examples thereof include a method of directly heating using a hot air heater or an infrared heater, a method of immersing the polymer piezoelectric material in a liquid such as heated silicon oil, and the like. At this time, if the polymer piezoelectric material is deformed by linear expansion, it is difficult to obtain a practically flat film. Therefore, a certain tensile stress (for example, 0.01 MPa to 100 MPa) is applied to the polymer piezoelectric material, It is preferable to apply temperature while preventing the piezoelectric polymer material from sagging.

  The temperature application time for the annealing treatment is preferably 1 second to 60 minutes, more preferably 1 second to 300 seconds, and further preferably heating in the range of 1 second to 60 seconds. When annealing is performed for more than 60 minutes, the degree of orientation may decrease due to the growth of spherulites from the molecular chains of the amorphous portion at a temperature higher than the glass transition temperature of the polymeric piezoelectric material. May decrease.

The polymeric piezoelectric material annealed as described above is preferably cooled rapidly after the annealing treatment.
In the annealing process, “rapidly cool” means that the annealed polymer piezoelectric material is immersed in ice water or the like immediately after the annealing process and cooled to at least the glass transition point Tg or less. It means that no other treatment is included in the dipping time.

The rapid cooling method includes a method of immersing the annealed polymer piezoelectric material in a coolant such as ethanol, methanol, or liquid nitrogen containing water, ice water, ethanol, or dry ice, or by spraying a liquid spray with a low vapor pressure to evaporate. The method of cooling by latent heat is mentioned.
To continuously cool the polymer piezoelectric material, it is possible to rapidly cool the polymer piezoelectric material by bringing it into contact with a metal roll controlled to a temperature not higher than the glass transition temperature Tg of the polymer piezoelectric material. It is. Further, the number of times of cooling may be only once, or may be two or more. Furthermore, annealing and cooling can be alternately repeated. In addition, when the annealing is performed on the polymer piezoelectric material that has been subjected to the above-described stretching treatment, the polymer piezoelectric material after the annealing may shrink as compared to before the annealing.

-Second Embodiment-
A second embodiment of the method for producing a polymeric piezoelectric material of the present invention includes a step of stretching a sheet containing an optically active polymer (preferably an amorphous sheet) mainly in a uniaxial direction, an annealing step, Are included in this order.
In the second embodiment, the step of stretching mainly in the uniaxial direction is a step of performing at least main stretching (further performing secondary stretching if necessary).
In the second embodiment, each condition of the step of extending mainly in the uniaxial direction and the annealing treatment step is such that the crystallinity of the polymer piezoelectric material to be produced is 20% to 80%, and the normalized molecule The product of the orientation MORc and the crystallinity is appropriately adjusted to be 25 to 250.
In addition, the preferable conditions of the step of extending mainly in the uniaxial direction and the annealing treatment step in the second embodiment are the same as the conditions of the second step and the annealing treatment step in the first embodiment, respectively.
In the second embodiment, it is not necessary to provide the first step (preliminary crystallization step) in the first embodiment.

<Applications of polymeric piezoelectric materials>
Polymeric piezoelectric material of the present invention, or large piezoelectric constant d ₁₄ is as described, transparency, because it is excellent piezoelectric material vertically tear strength, speakers, headphones, a touch panel, remote controller, microphone, water microphone, Ultrasonic transducer, ultrasonic applied measuring instrument, piezoelectric vibrator, mechanical filter, piezoelectric transformer, delay device, sensor, acceleration sensor, impact sensor, vibration sensor, pressure sensor, tactile sensor, electric field sensor, sound pressure sensor, display It can be used in various fields such as fans, pumps, variable focus mirrors, sound insulation materials, sound insulation materials, keyboards, acoustic equipment, information processing equipment, measurement equipment, medical equipment, and the like.

  At this time, the polymeric piezoelectric material of the present invention is preferably used as a piezoelectric element having at least two surfaces and electrodes provided on the surfaces. The electrodes only need to be provided on at least two surfaces of the polymeric piezoelectric material. Although it does not restrict | limit especially as said electrode, For example, ITO, ZnO, IZO (trademark), a conductive polymer, etc. are used.

Further, the polymer piezoelectric material of the present invention and an electrode can be repeatedly stacked and used as a laminated piezoelectric element. As an example, a unit in which an electrode and a polymer piezoelectric material are repeatedly stacked, and the main surface of the polymer piezoelectric material that is not covered with an electrode is covered with an electrode. Specifically, the unit having two repetitions is a laminated piezoelectric element in which electrodes, polymer piezoelectric material, electrodes, polymer piezoelectric material, and electrodes are stacked in this order. Of the polymer piezoelectric materials used in the laminated piezoelectric element, one layer of the polymer piezoelectric material may be the polymer piezoelectric material of the present invention, and the other layers may not be the polymer piezoelectric material of the present invention.
Further, when the laminated piezoelectric element includes a plurality of polymer piezoelectric materials of the present invention, if the optical activity of the optically active polymer contained in one layer of the polymer piezoelectric material of the present invention is L, the other layers The optically active polymer contained in this polymeric piezoelectric material may be L-form or D-form. The arrangement of the polymeric piezoelectric material can be appropriately adjusted according to the use of the piezoelectric element.

  For example, a first layer of a piezoelectric polymer material containing an L-type optically active polymer as a main component is laminated with a second polymeric piezoelectric material containing an L-type optically active polymer as a main component via an electrode. When the uniaxial stretching direction (main stretching direction) of the first polymeric piezoelectric material intersects, preferably orthogonally intersects, the uniaxial stretching direction (main stretching direction) of the second polymeric piezoelectric material, It is preferable because the direction of displacement between the polymeric piezoelectric material and the second polymeric piezoelectric material can be made uniform, and the piezoelectricity of the entire laminated piezoelectric element is enhanced.

  On the other hand, the first layer of the polymeric piezoelectric material containing the L-type optically active polymer as the main component is laminated with the second polymeric piezoelectric material containing the D-type optically active polymer as the main component via the electrode. The first uniaxial stretching direction (main stretching direction) of the first polymeric piezoelectric material is arranged so as to be substantially parallel to the uniaxial stretching direction (main stretching direction) of the second polymeric piezoelectric material. This is preferable because the directions of displacement of the polymeric piezoelectric material and the second polymeric piezoelectric material can be made uniform, and the piezoelectricity of the entire laminated piezoelectric element is enhanced.

  In particular, when an electrode is provided on the main surface of the polymeric piezoelectric material, it is preferable to provide a transparent electrode. Here, the transparency of the electrode specifically means that the internal haze is 40% or less (total light transmittance is 60% or more).

  The piezoelectric element using the polymeric piezoelectric material of the present invention can be applied to the above-described various piezoelectric devices such as speakers and touch panels. In particular, a piezoelectric element provided with a transparent electrode is suitable for application to a speaker, a touch panel, an actuator, and the like.

  Hereinafter, the embodiment of the present invention will be described more specifically by way of examples. However, the present embodiment is not limited to the following examples unless it exceeds the gist of the present invention.

[Example 1]
A polylactic acid resin (registered trademark LACEEA, H-400 (weight average molecular weight Mw: 200,000)) manufactured by Mitsui Chemicals, Inc. is put into an extruder hopper and extruded from a T-die while heating at 220 to 230 ° C. A pre-crystallized sheet having a thickness of 230 μm was formed by contact with a cast roll at 0 ° C. for 0.3 minutes (pre-crystallization step) The crystallinity of the pre-crystallized sheet was measured and found to be 4%.
Simultaneously up to 3.0 times (main stretching) in the TD direction by the tenter method and 2.0 times (secondary stretching) in the MD direction by the roll-to-roll method while heating the obtained pre-crystallized sheet at 80 ° C. Biaxial stretching was performed to obtain a film (stretching step).
The film after the stretching step was brought into contact with a roll heated to 145 ° C. by roll-to-roll, annealed, and rapidly cooled to produce a polymer piezoelectric material (annealing step). The rapid cooling is performed by rapidly lowering the film temperature to near room temperature by bringing the annealed film into contact with the air at 20 ° C. to 30 ° C. and then contacting with the metal roll of the film winder. It was.

[Examples 2-8, Comparative Examples 1-2]
Subsequently, in the production of the polymeric piezoelectric material of Example 1, the precrystallization conditions and the stretching conditions were changed to the conditions shown in Table 1 in the same manner as in Examples 2-8 and Comparative Examples 1-2. A molecular piezoelectric material was prepared.
In Examples 5 to 8, the main stretching direction was the MD direction, and the secondary stretching direction was the TD direction.

-Measurement of L and D amounts of resin (optically active polymer)-
A sample (polymer piezoelectric material) of 1.0 g was weighed into a 50 mL Erlenmeyer flask, and 2.5 mL of IPA (isopropyl alcohol) and 5 mL of 5.0 mol / L sodium hydroxide solution were added. Next, the Erlenmeyer flask containing the sample solution was placed in a water bath at a temperature of 40 ° C. and stirred for about 5 hours until the polylactic acid was completely hydrolyzed.

The sample solution was cooled to room temperature, neutralized by adding 20 mL of 1.0 mol / L hydrochloric acid solution, and the Erlenmeyer flask was sealed and mixed well. 1.0 mL of the sample solution was placed in a 25 mL volumetric flask, and HPLC sample solution 1 was prepared with 25 mL of mobile phase. 5 μL of the HPLC sample solution 1 was injected into the HPLC apparatus, the D / L body peak area of polylactic acid was determined under the following HPLC conditions, and the amount of L body and the amount of D body were calculated.
-HPLC measurement conditions-
・ Column Optical resolution column, SUMICHIRAL OA5000 manufactured by Sumika Chemical Analysis Co., Ltd.
・ Measuring device: JASCO Corporation liquid chromatography column temperature: 25 ℃
Mobile phase 1.0 mM-copper (II) sulfate buffer / IPA = 98/2 (V / V)
Copper (II) sulfate / IPA / water = 156.4 mg / 20 mL / 980 mL
・ Mobile phase flow rate 1.0ml / min ・ Detector UV detector (UV254nm)

<Molecular weight distribution>
Using a gel permeation chromatograph (GPC), the molecular weight distribution (Mw / Mn) of the resin (optically active polymer) contained in each polymer piezoelectric material of Examples and Comparative Examples was measured by the following GPC measurement method.
-GPC measurement method-
・ Measurement device Waters GPC-100
・ Column Showa Denko KK, Shodex LF-804
-Preparation of sample Each polymeric piezoelectric material of an Example and a comparative example was dissolved in the solvent [chloroform] at 40 degreeC, respectively, and the sample solution with a density | concentration of 1 mg / ml was prepared.
Measurement conditions 0.1 ml of the sample solution was introduced into the column at a solvent (chloroform), a temperature of 40 ° C. and a flow rate of 1 ml / min, and the sample concentration in the sample solution separated by the column was measured with a differential refractometer. For the molecular weight of the resin, a universal calibration curve was prepared using a polystyrene standard sample, and the weight average molecular weight (Mw) of each resin was calculated. Table 1 shows the measurement results of the resins used in the examples and comparative examples. In Table 1, “LA” represents LACEA H-400.

<Measurement and evaluation of physical properties>
For the polymeric piezoelectric materials of Examples 1-8 and Comparative Examples 1-2 obtained as described above, glass transition temperature Tg, melting point Tm, crystallinity, specific heat capacity Cp, thickness, internal haze, The piezoelectric constant, MORc, and dimensional change rate were measured, and longitudinal fissure evaluation was performed.
The evaluation results are shown in Table 2.
Specifically, the measurement was performed as follows.

[Glass transition temperature Tg, melting point Tm, and crystallinity]
Each of the polymeric piezoelectric materials of Examples and Comparative Examples was accurately weighed 10 mg each, and measured using a differential scanning calorimeter (DSC-1 manufactured by Perkin Elmer Co., Ltd.) at a temperature rising rate of 10 ° C./min. A melting endotherm curve was obtained. From the obtained melting endotherm curve, melting point Tm, glass transition temperature Tg, specific heat capacity Cp and crystallinity were obtained.

[Specific heat capacity Cp]
When each of the polymeric piezoelectric materials of Examples and Comparative Examples was measured with the above differential scanning calorimeter, the amount of heat required to raise 1 ° C. per gram was measured. Measurement conditions were the same as Tg and Tm.

[Dimensional change rate]
Each polymeric piezoelectric material of the example and the comparative example was cut by 50 mm in the MD direction and 50 mm in the TD direction to cut out a rectangular film of 50 mm × 50 mm. This film was suspended in an oven set at 85 ° C. and annealed for 30 minutes (hereinafter, this annealing treatment for evaluating the dimensional change rate was referred to as “anneal B”). Thereafter, the dimension of the film rectangular side length in the MD direction before and after annealing B was measured with calipers, the dimensional change rate (%) was calculated according to the following formula, and the dimensional stability was evaluated based on the absolute value. A smaller dimensional change rate indicates higher dimensional stability.
Dimensional change rate (%) = 100 × ((side length in MD direction before annealing B) − (side length in MD direction after annealing B)) / (side length in MD direction before annealing B)

[Internal haze]
The “internal haze” referred to in the present application refers to the internal haze of the polymeric piezoelectric material of the present invention, and the measurement method is a general method.
Specifically, the internal haze (hereinafter also referred to as internal haze (H1)) of each of the polymer piezoelectric materials of Examples and Comparative Examples was measured by measuring light transmittance in the thickness direction. More specifically, the haze (H2) is measured in advance by sandwiching only silicon oil (Shin-Etsu Chemical Co., Ltd., Shin-Etsu Silicone (trademark), model number: KF96-100CS) between two glass plates. A film (polymer piezoelectric material) whose surface is uniformly coated with oil is sandwiched between two glass plates, and the haze (H3) is measured. By taking these differences as shown in the following formulas, examples and comparative examples The internal haze (H1) of each polymeric piezoelectric material was obtained.
Internal haze (H1) = Haze (H3) -Haze (H2)

The haze (H2) and haze (H3) in the above formula were measured by measuring the light transmittance in the thickness direction using the following apparatus under the following measurement conditions.
Measuring device: manufactured by Tokyo Denshoku Co., Ltd., HAZE METER TC-HIIIDPK
Sample size: 30 mm wide x 30 mm long (see Table 2 for thickness)
Measurement conditions: Conforms to JIS-K7105 Measurement temperature: Room temperature (25 ° C.)

[Piezoelectric constant d ₁₄ (by displacement method)]
A 40 mm × 40 mm test piece (polymer piezoelectric material) having an Ag conductive layer formed on both sides is formed in a direction of 45 mm and a direction of 45 ° with respect to the stretching direction (MD direction) of the polymer piezoelectric material. A rectangular film of 32 mm × 5 mm was cut into 5 mm in the orthogonal direction. This was used as a piezoelectric constant measurement sample. When a sine wave AC voltage of 10 Hz and 300 Vpp was applied to the obtained sample, the difference distance between the maximum value and the minimum value of the displacement of the film was measured with a laser spectral interference displacement meter SI-1000 manufactured by Keyence Corporation. . The value obtained by dividing the measured displacement (mp-p) by the reference length of the film of 30 mm is used as the amount of distortion, and the electric field intensity ((applied voltage (V)) / (film thickness)) applied to the film. A value obtained by multiplying the value divided by 2 by 2 was defined as a piezoelectric constant d ₁₄ (pm / V).

[Standardized molecular orientation MORc]
About each polymeric piezoelectric material of an Example and a comparative example, normalization molecular orientation MORc was measured by Oji Scientific Instruments Co., Ltd. microwave system molecular orientation meter MOA-6000. The reference thickness tc was set to 50 μm.

(Vertical fissure evaluation)
About each polymeric piezoelectric material of an Example and a comparative example, based on the test method "right-angled tear method" described in "Tear strength of a plastic film and a sheet | seat" of JISK7128-3, tear strength of MD direction The longitudinal tearability was evaluated by measuring the thickness and tear strength in the TD direction.
In the longitudinal tear evaluation, when the tear strength in the MD direction and the tear strength in the TD direction are both large, it means that the decrease in the longitudinal tear strength is suppressed. In other words, the fact that at least one of the tear strength in the MD direction and the tear strength in the TD direction is low means that the longitudinal tear strength has decreased.
In the measurement of tear strength, the crosshead speed of the tensile tester was 200 mm per minute.
The tear strength (T) was calculated from the following equation.
T = F / d
In the above formula, T represents the tear strength (N / mm), F represents the maximum tear load, and d represents the thickness (mm) of the test piece.

As shown in Table 2, in Examples 1 to 8, as compared with Comparative Example 1, a decrease in longitudinal tear strength (here, tear strength in the MD direction) was suppressed.
Moreover, in Examples 1-8, it was excellent in transparency (namely, internal haze is low), and showed the high piezoelectric constant (1 pm / V or more).
On the other hand, in Comparative Example 2, the piezoelectric constants were almost the same as in Examples 1 to 8, but the longitudinal tear strength (here, the tear strength in the MD direction) was lower than in Examples 1 to 8.
In Table 2, “ND” indicates that there is no measurement result because measurement is omitted.

The disclosure of Japanese application 2011-272708 is incorporated herein by reference in its entirety.
All documents, patent applications, and technical standards mentioned in this specification are to the same extent as if each individual document, patent application, and technical standard were specifically and individually described to be incorporated by reference, Incorporated herein by reference.

Claims (13)

  Including a helical chiral polymer having an optical activity of weight average molecular weight of 50,000 to 1,000,000, crystallinity obtained by DSC method is 20% to 80%, and measured with a microwave transmission type molecular orientation meter A polymer piezoelectric material, wherein the product of the normalized molecular orientation MORc and the crystallinity when the reference thickness is 50 μm is 25 to 250.   The polymeric piezoelectric material according to claim 1, wherein the crystallinity is 40.8% or less. The polymeric piezoelectric material according to claim 1 or 2 , wherein an internal haze with respect to visible light is 40% or less. The polymeric piezoelectric material according to any one of claims 1 to 3, wherein the normalized molecular orientation MORc is 1.0 to 15.0. Piezoelectric constant d ₁₄ measured by a displacement method at 25 ° C. is 1 Pm/V or more, polymeric piezoelectric material according to any one of claims 1 to 4. The polymer piezoelectric according to any one of claims 1 to 5, wherein the helical chiral polymer is a polylactic acid polymer having a main chain including a repeating unit represented by the following formula (1). material.
The polymeric piezoelectric material according to any one of claims 1 to 6, wherein the helical chiral polymer has an optical purity of 95.00% ee or higher. The polymeric piezoelectric material according to any one of claims 1 to 7, wherein a content of the helical chiral polymer is 80% by mass or more. The polymeric piezoelectric material according to any one of claims 1 to 8, wherein an internal haze with respect to visible light is 1.0% or less. A method for producing the polymeric piezoelectric material according to any one of claims 1 to 9,
A first step of heating a non-crystalline sheet containing the helical chiral polymer to obtain a pre-crystallized sheet, and a second step of simultaneously stretching the pre-crystallized sheet in biaxial directions. A method for producing a polymeric piezoelectric material. In the first step of obtaining the pre-crystallized sheet, the amorphous sheet is heated until the crystallinity becomes 1% to 70% at a temperature T represented by the following formula. A method for producing a polymeric piezoelectric material.
Tg−40 ° C. ≦ T ≦ Tg + 40 ° C.
(Tg represents the glass transition temperature of the helical chiral polymer.) Wherein in a first step of obtaining a pre-crystallized sheet, wherein at 20 ° C. to 170 ° C. The amorphous state sheet comprising polylactic acid as a helical chiral polymer, heated for 5 seconds to 60 minutes, according to claim 10 or claim 11. A method for producing a polymeric piezoelectric material according to 11 . The method for producing a polymeric piezoelectric material according to any one of claims 10 to 12 , wherein annealing is performed after the second step.